The Sm (CoFeCuZr)_z permanent magnets with different z values (z=7.5~8.5) were prepared by powder metallurgy. The properties, constituent phase, precipitated-phase content, microstructure and element distribution of the magnet were characterized by magnetic measurement system, X ray diffraction analysis, electron probe and transmission electron microscope. Magnetic properties change with z value, and the inherent mechanism is explained in this essay. The results show that the increase of z value leads to the increase in the size of cell structure and the 2:17R phase with high saturation magnetization, which finally results in the improvement of remanence B_r. The precipitated Zr-riched phase increases with the z value increases, which has a weakening effect on the squareness H_k/H_cj. The z value changes the enrichment of Cu element at the edge of 2: 17R phase, which has a significant effect to the coercivity H_cj. Within the certain range (z <8.2), the higher the content of Cu at that edge, the larger the coercivity is.